The present invention relates to electrophotographic copiers for copying books, sheets of documents and the like, more particularly to an electrophotographic copier of the transfer type which employs the Carlson system for the formation of the image and in which the image of an original document placed on a transparent document table is continuously projected onto a photoreceptor on a rotating or moving endless support by an exposure optical system of the slit scanning type and the latent image of the document thus formed is then rendered visible with a toner and transferred onto ordinary paper.
The copier of this type is known by the trade name of "Xerox 914," etc. However, the copiers heretofore known have the following drawback:
1. Since the photoreceptor is integrally formed on the surface of a drum by a vacuum evaporation, the photoreceptor has to be replaced together with the drum when the photoreceptor gets deteriorated, hence the replacement of the photoreceptor is expensive. PA1 2. With the exposure optical system of the slit scanning type, the document illuminating system and projecting lens have to be travelled in parallel with the document at a speed proportional to the peripheral speed of the photoreceptor on the drum. Consequently, the exposure is not always effected with principal rays from the lens and the varying length of the light path from the original to the photoreceptor requires an exposure optical system which occupies a large space relative to the length of the original. Thus the copier becomes inevitably large.
Further when employing a system of the foregoing type, it is generally difficult to provide copiers capable of copying documents of a large size, for example, those measuring 11 .times. 14 inches or 14 .times. 17 inches and to make copies with a clear image.